If your non-slip knot is breaking at the clinch, then you have slippage. This is a function of not using enough turns in the clinch portion of the knot. Four wraps for tippets of 0.016" dia., or under, three wraps for tippets 0.017" to 0.030" and two wraps when over 0.030". Break strength is 95% to 100%. When 100% strength is needed use four to five wraps.
The above info is from Bill Nash. He is the knot guru that most defer to for objective flyfishing knots/systems.